1. Field of the Invention
The present invention relates to a data relay apparatus and a data relay method to relay data in a network, which carries out a failure recovery, when a failure occurs at any point on a working path that is being used as a path through which data is transferred via a plurality of data relay apparatuses, by switching the path to a backup path to make a detour to avoid the failure point, and more particularly to a data relay apparatus and a data relay method that can reduce the number of path used to recover the failure by increasing the number of working paths that can be handled by a single path used to recover the failure, such as a monitor path.
2. Description of the Related Art
The generalized multi-protocol label switching (GMPLS)/MPLS is a technology to transfer data according to label information. The label information includes a fixed-length label that is attached to a head of a packet, a time slot in a time division transmission, and an optical wavelength in an optical-multiplexed transmission. In particular, a network in which data is transferred using the fixed-length label that is attached to a head of a packet is referred to as the MPLS. In addition, the GMPLS network uses a single piece or a plurality of pieces of information including the fixed-length label used in the MPLS network.
For example, in a packet transmission using the fixed-length label, a relay node (a label switch router (LSR)) holds a label table that represents a relation of an output label and an output interface (IF) with respect to an input label and an input IF. At a time of packet relay, an output IF is determined according to a label attached to a packet received, instead of an address. Then, the label attached to the packet is rewritten into the output label to be relayed. By repeating this procedure, the packet is transmitted to a destination. A relay node (start-point node) of the MPLS network attaches the label at the beginning. The MPLS is such kind of high-speed packet relay technology.
FIG. 34 is a schematic diagram for explaining a packet transmission using the fixed-length label. The figure illustrates an example of transferring a packet from LSR1 to LSR4. First of all, the LSR1 attaches a label a to the packet to be transferred. An LSR2 receives the packet having the label a from an IF#1, searches for a label table, and acquires an output IF and an output label. After that, the LSR2 rewrites the label of the packet into an output label, and outputs the packet to an output IF. The MPLS transfers the packet to the LSR4 of an end-point by repeating such kind of process at each of the LSRs.
In this manner, the MPLS can enhance the speed of the packet relay by transferring the packet according to the fixed-length label. In addition, the MPLS can assure a bandwidth for each of the packet flows by associating a bandwidth control in the relay node with each of the labels.
Furthermore, in the time division transmission, each of the nodes holds a label table that represents a relation of an output label and an output IF with respect to an input label and an input IF. Then, each of the nodes determines an output IF and an output time slot according to a reception IF and a reception time slot, and outputs data to the output time slot of the output IF. By repeating this procedure, the data is transmitted to a destination.
Moreover, in the optical-multiplexed transmission, each of the nodes holds a label table that represents a relation of an output optical wavelength and an output IF with respect to an input optical wavelength and an input IF. Then, each of the nodes determines an output IF and an output optical wavelength according to a reception IF and a reception optical wavelength, converts the reception optical wavelength into the output optical wavelength, and outputs the output optical wavelength to the output IF. By repeating this procedure, the data is transmitted to a destination.
The GMPLS is a technology to carry out a data transfer in the same mechanism by handling the fixed-length label, the time slot, and the optical wavelength as a label.
In the GMPLS/MPLS, it is necessary to build a label table at each of the nodes, and a path-establishing signal protocol (such as CR-LDP/RSVP-TE) is used for building the label table. The following is an explanation of an operation for a path establishment with the RSVP-TE as an example.
FIG. 35 is a schematic diagram for explaining an operation of the path-establishing signal protocol (RSVP-TE). As shown in the figure, a start-point node that requests a path establishment transmits a request message for the path establishment (Path message) to an end-point node of the path by Hop-by-Hop. In the schematic diagram shown in FIG. 35, information on a relay node to be routed through is inserted in the Path message, for designating a path explicitly.
The end-point node that receives the Path message returns a path-establishment response message (Resv message) to carry out an assignment of the label to the start-point node along the path through which the Path message is transmitted. At this moment, a label table for transferring data is built by registering a label stored in the Resv message to the label table. A path ID is stored in both of the Path message and the Resv message, and the path ID is also registered to the label table accordingly.
In the path-establishment signal protocol, a PathErr/ResvTear/Notify message is used as a failure message for notifying that a failure has occurred in a path established, in addition to the Path message indicating a request for a path establishment and the Resv message that is a response to the Path message.
FIG. 36 is a schematic diagram for illustrating a transfer of a failure message using a PathErr/ResvTear message. As shown in the figure, the PathErr/ResvTear message is transferred to the start-point node by Hop-by-Hop along the path. On the other hand, a Notify message is directly transferred to the start-point node that is a destination for a message. For this reason, the Notify message may also arrives at the start-point node along a route that is different from the path. In the failure message, the same path ID as the path ID stored in the Path/Resv message, so that it is possible to carry out an association between the failure and the path.
In the GMPLS/MPLS, when a failure occurs in a working path for transferring data, the transfer of the data is carried out using a backup path that makes a detour around the working path. For example, in the MPLS, the working path is monitored using a monitoring path, and when a failure occurs in the working path, a failure recovery process is carried out by switching the working path to a backup path (see, for example, Japanese Patent Application Laid-Open Publication No. 2003-338831).
FIG. 37 is a schematic diagram for explaining a failure recovery method using a monitoring path. As shown in the figure, in the failure recovery using the monitoring path, a working path and a backup path for making a traffic on the working path take a detour at a time of a failure occurrence, using the path-establishment signaling protocol. At this moment, the backup path is established between the same start-point node and end-point node as those of the working path.
Furthermore, a monitoring path for monitoring a status of the working path is established using the path-establishment signaling protocol. The monitoring path includes, as shown in FIG. 37, two paths in both a downstream direction and an upstream direction along the working path. A monitoring packet is reciprocated on the two monitoring paths periodically. This monitoring packet is a labeled packet because it is transmitted on the monitoring path.
When there is a failure on the working path, the start-point node “LSR1” detects the failure by one of the following methods. One of the methods is to detect the failure by a fact that the monitoring packet that is supposed to be transmitted and received periodically does not arrive within a predetermined time. Another method is to detect the failure by a relay node on the upstream, and to transfer a failure notification packet with a labeled packet by the relay node.
Upon recognizing that a failure has occurred by one of the above two methods, the start-point node transmits the traffic that was being transmitted to the working path to the backup path to make a detour around the failure. One monitoring path can be established for a plurality of working paths that is established on the same route, as shown in FIG. 37. This will decrease a total number of the monitoring paths.
However, in the conventional technology described above, since the backup path is limited to a plurality of paths having the same route only, it is not possible to increase the number of the working paths that can be handled with one monitoring path. For this reason, the number of the monitoring paths is inevitably increased.
Furthermore, the fact that it is necessary to establish two monitoring paths for one sector is another factor for increasing the number of the monitoring paths. In consequence, the number of the monitoring paths to be managed on a network is increased, resulting in an increase of a management load.
Moreover, since it is necessary to transmit and receive the monitoring packet periodically, the monitoring packet consumes a bandwidth even for a normal time. In addition, since the notification packet for notifying the failure is inserted from the relay node, not from an entrance node of the path, it is necessary to install a function for inserting a packet from a relay node of the path.
It is an object of the present invention to solve the above problems in the conventional technology and to provide a data relay apparatus and a data relay method that can reduce the number of paths for a recovery of a failure by increasing the number of working paths that can be handled by a single path for the recovery of the failure, such as a monitoring path.
As a failure recovery method, there are several methods disclosed so far, such as a path detour method using an error message of the signaling protocol, a fast rerouting method explored by IETF (Internet Draft: draft-iert-mpls-rsvp-lsp-fastreroute-07.txt), and a path detour method using a multiple addressing of failure information (Yasuki fujii, Keiji Miyazaki, Kohei Iseda, “Review of preplan-type failure recovery method”, Singakugiho TM2000-60, pp. 67-72, November 2000).
However, the path detour method using the signaling protocol has a problem that, when a failure that affects a plurality of paths occurs, a number of message are generated, which increases a network load. The fast rerouting method has a problem of increasing the number of backup paths because it is necessary to establish the same number of backup paths as the number of links through which the working path passes. The path detour method using the multiple addressing of the failure information has a problem that a packet to an unrelated node is generated because a multiple-address packet is used.